过冷奥氏体转变时原子位移规律

Atomic displacement law of the supercooled Austenite transformation

研究过冷奥氏体转变时原子的位移方式具有重要理论价值.原子位移方式不同是区别相变机制的依据之一.过冷奥氏体转变为珠光体、贝氏体、马氏体等组织,最基本的区别是原子位移方式的不同,从高温到低温,原子位移方式是逐渐演化的.研究表明,三个相变中原子位移方式分别是:(1)高温区的共析分解是扩散型相变,原子每次位移距离为一个原子间距.界面扩散是主要位移方式;(2)贝氏体相变是过渡性相变,贝氏体铁素体的形成是无扩散过程,而贝氏体碳化物的形成是扩散过程.铁原子和替换原子进行热激活跃迁位移.原子位移距离小于一个原子间距,各原子位移矢量不等,界面控制.(3)马氏体相变是无扩散的,所有原子进行集体协同位移,原子每次移动距离远远小于一个原子间距.切变机制不正确.在晶格改组过程中,为调整应变能一般需要形成位错、孪晶或层错等亚结构.

It is theoretically significant to study the atomic displacement mode during the supercooled austenite transformation. The difference of the atomic displacement mode can be served as the important criterion of the phase transformation mechanism. With the decrease of the temperature, the supercooled austenite can be transformed to pearlite, bainite and Martensite, the most fundamental difference of which is that the atomic displacement evolves gradually from high to low temperature. The studies show that the atomic displacement modes of the three kinds of phase transformation are as follows： （ 1 ） the eutectoid decomposition in the high temperature region is the diffusion transformation ,where every displacement distance of the atoms is an atomic spacing. The interfacial diffusion is the main displacement mode. （2） The bainite phase transformation is the transitional transformation, in which the formation of the bainite ferrite is a diffusionless process but the formation of the bainite carbide is a diffusional one. The atomic displacement mode of iron and replace atoms belongs to heat activation transition. The every displacement distance of the atoms is less than an atomic spacing. The displacement vector of every atom is unequal, which is an interface controlled process. （3） The martensite phase transformation is diffusionless, in which the atomic displacement mode of all atoms is the collective collaborative displacement and the every displacement distance of the atoms is far less than that of an atomic spacing. The shear mechanism is incorrect. During the crystal lattice reconstruction, the substructure of the dislocation, twin crystal or stacking fault can generally come into being to adjust the strain energy.